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[ Upstream commitb24335521d] selftests/memfd: use IPC semaphore instead of SIGSTOP/SIGCONT In order to synchronize new processes to test inheritance of memfd_noexec sysctl, memfd_test sets up the sysctl with a value before creating the new process. The new process then sends itself a SIGSTOP in order to wait for the parent to flip the sysctl value and send a SIGCONT signal. This would work as intended if it wasn't the fact that the new process is being created with CLONE_NEWPID, which creates a new PID namespace and the new process has PID 1 in this namespace. There're restrictions on sending signals to PID 1 and, although it's relaxed for other than root PID namespace, it's biting us here. In this specific case the SIGSTOP sent by the new process is ignored (no error to kill() is returned) and it never stops its execution. This is usually not noticiable as the parent usually manages to set the new sysctl value before the child has a chance to run and the test succeeds. But if you run the test in a loop, it eventually reproduces: while [ 1 ]; do ./memfd_test >log 2>&1 || break; done; cat log So this patch replaces the SIGSTOP/SIGCONT synchronization with IPC semaphore. Link: https://lkml.kernel.org/r/a7776389-b3d6-4b18-b438-0b0e3ed1fd3b@work Fixes:6469b66e3f("selftests: improve vm.memfd_noexec sysctl tests") Signed-off-by: Aristeu Rozanski <aris@redhat.com> Cc: Aleksa Sarai <cyphar@cyphar.com> Cc: Shuah Khan <shuah@kernel.org> Cc: liuye <liuye@kylinos.cn> Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Sasha Levin <sashal@kernel.org>